The visual system allows the eye to focus light rays into meaningful images. The most common problem an ophthalmologist or optometrist will encounter is that of spherical ammetropia, or the formation of an image by the eye which is out of focus with accommodation due to an improperly shaped globe. The ophthalmologist or optometrist determines the refractive status of the eye and corrects the optical error with contact lenses or glasses.
Many procedures have been developed to correct spherical ammetropia by modifying the shape of the cornea. Light entering the eye is first focused by the cornea, which possesses approximately 75% of the eye's overall refractory power. The majority of refractive operations involve either decreasing or increasing the anterior curvature of the cornea.
The procedures in early corneal refractive surgery such as keratophakia and keratomileusis were originally developed to correct myopia and involved removing a corneal disc from the patient with a microkeratome. The removed corneal disc was then frozen prior to reshaping the posterior surface with a cryolathe. After thawing, the disc was returned to the eye and secured with sutures.
Epikeratophakia, as described in U.S. Pat. No. 4,662,881, is a procedure that involves inserting a precut donor corneal tissue lens with beveled edges into corresponding grooves in recipient cornea. The lens is then sutured to the corneal bed. The donor lens is lyophilized and requires rehydration before placement on recipient cornea.
These techniques and their variations were generally considered to be unsuccessful due to frequent complications involving irregular astigmatism, delayed surgical healing, corneal scarring, and instability of the refractive result. The problems were attributed to the technical complexity of the procedures as well as to the distortion in architecture of the corneal tissue secondary to lens manipulation. For example, in epikeratophakia, epithelial irregularity is induced by lyophilization of the donor lens. Freezing of the lenticule in keratophakia and keratomileusis also causes severe damage to epithelial and stromal cells and disrupts the lamellar architecture of the cornea.
The present invention is a pre-fabricated lens made of donor corneal tissue obtained from tissue sources such as human or animal cornea. The lens is a corneal disc that is preferably shaped on the posterior surface generally to conform in shape to the eye's anterior surface. The inventive lens may be shaped by an ablative laser, e.g., by an excimer laser or other suitable laser. The corneal lenticule is living tissue that has not been frozen, lyophilized, or chemically modified, e.g., fixed with glutaraldehyde to crosslink corneal tissue. Pre-existing keratocytes are removed and then replaced with human keratocytes to decrease antigenicity. After removal of epithelium in the central zone of the recipient's cornea, the lens is placed on this zone in the same manner that a contact lens is placed on the eye.
Ocular lenses found in the prior art do not use native cornea, but are formulated using soluble collagen such as collagen hydrogels, e.g., polyhydroxyethylmethacrylate, or other biocompatible materials. For example, in U.S. Pat. No. 5,213,720, to Civerchia, soluble collagen is gelled and crosslinked to produce an artificial lens. In addition to hydrogels, U.S. Pat. No. 4,715,858, to Lindstrom, discloses lenses made from various polymers, silicone, and cellulose acetate butyrate.
In the cases where ocular lenses use corneal tissue, the lenses are either corneal implants or require a separate agent to adhere the lens to the corneal bed. U.S. Pat. No. 5,171,318, to Gibson et al., and U.S. Pat. No. 5,919,185, to Peyman, relate to a disc of corneal tissue that is partially or entirely embedded in stroma. The ocular lens device disclosed in U.S. Pat. No. 4,646,720, to Peyman et al., and U.S. Pat. No. 5,192,316, to Ting, is attached to recipient cornea with sutures. The corneal inlay described in U.S. Pat. No. 4,676,790, to Kern, is bonded to recipient cornea using sutures, laser welding, or application of a liquid adhesive or crosslinking solution.
The ocular lens device of this invention does not alter the anatomical structure of corneal tissue. U.S. Pat. No. 4,346,482, to Tennant et al., discloses a “living contact lens” consisting of donor cornea that has been anteriorly curved for correction of vision. However, this lens is frozen prior to reshaping on a lathe which results in stromal keratocyte death. U.S. Pat. No. 4,793,344, to Cumming et al., also describes a donor corneal tissue lens that is modified by treatment with a glutaraldehyde fixative that preserves the tissue and prevents lens swelling. This treatment alters the basic structure of the corneal lenticule by crosslinking the tissue.
Furthermore, the cited documents do not show any methods of lens preparation that remove native corneal tissue cells and replace them with cells cultivated from human cornea. My inventive device is devitalized of native epithelium and keratocytes to create an acellular corneal tissue, and then revitalized with human epithelium and keratocytes. An attempt to construct a so-called “corneal tissue equivalent” was shown in U.S. Pat. No. 5,374,515, to Parenteau et al. However, the collagen used in that “equivalent” is obtained from bovine tendon instead of from cornea. The added keratocytes and epithelium are also not from human sources. The tissue using these cell culturing procedures is also quite fragile.
An excimer laser is used to reform a cornea via the “laser in situ keratomileusis” (LASIK) procedure. In this technique, an excimer laser is used to perform stromal photoablation of a corneal flap or in situ photoablation of the exposed stromal bed. Studies have shown that the inaccuracy of correction by this procedure may be as much as one diopter from the desired value. Lenses (contacts and spectacles), in contrast, are able to correct within 0.25 diopters of the desired value.
U.S. Pat. No. 6,036,683, to Jean et al., shows the use of a laser to reshape the cornea. However, the laser changes the native structure of the cornea by irreversibly coagulating collagen. Post-laser relaxation of collagen is not possible with this treatment.
This invention, however, in some variations relates to a pre-fabricated donor contact lens that adheres to recipient cornea without sutures. The lens preserves the anatomy of normal corneal tissue. The donor lens may be obtained from human and animal sources, is devitalized of native keratocytes and epithelium to create an acellular tissue, and then optionally revitalized with at least one of human keratocytes and epithelial cells to maintain lens viability and decrease antigenicity. The inventive corneal overlay technique may be completed under local anesthesia as well as general anesthesia, and the availability of a precut lens will greatly decrease procedure time, patient cost, and risk of operative complications. The duration of healing will also be reduced due to the implementation of a lens already repopulated with keratocytes.
None of the cited documents shows or suggest my invention as described herein.